Traditionally, containers used for the storage of products for human consumption were made of glass. Typical desirable glass characteristics include transparency, indeformability and perfect label fixation. Nevertheless, because glass is fragile, easily breakable and heavy, it has become cost prohibitative, due to the high number of bottle breaks during handling. Moreover, as a result of breakage preventive measures and weight, the transportation expenses associated with glass greatly increases the cost of the product.
Numerous commodities previously supplied in glass containers are now being supplied in plastic containers, more specifically polyester and even more specifically polyethylene terephthalate (PET) containers. Manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities.
Manufacturers currently supply PET containers for various liquid commodities, such as beverages. Often these liquid products, such as juices and isotonics, are filled into the containers while the liquid product is at an elevated temperature, typically 68° C.–96° C. (155° F.–205° F.) and usually about 85° C. (185° F.). When packaged in this manner, the hot temperature of the liquid commodity is used to sterilize the container at the time of filling. This process is known as “hot filling”. The containers designed to withstand the process are known as “hot fill” or “heat set” containers.
The use of blow molded plastic containers for packaging hot fill beverages is well known. However, a container that is used for hot fill applications is subject to additional mechanical stresses on the container that result in the container being more likely to fail during storage or handling. For example, it has been found that the thin sidewalls of the container deform or collapse as the container is being filled with hot fluids. In addition, the rigidity of the container decreases immediately after the hot fill liquid is introduced into the container. After being hot filled, the heat set containers are capped and allowed to reside at generally about the filling temperature for approximately five (5) minutes. The containers, along with the product, are then actively cooled so that the filled container may be transferred to labeling, packaging and shipping operations. As the liquid cools, it evaporates and shrinks in volume. Thus, upon cooling, the volume of the liquid in the container is reduced. This product shrinkage phenomenon results in the creation of a negative pressure or vacuum within the container. Generally, this negative pressure or vacuum within the container ranges from 1–300 mm Hg less than atmospheric pressure (i.e., 759 mm Hg–460 mm Hg). If not controlled or otherwise accommodated, these negative pressures or vacuums result in deformation of the container which leads to either an aesthetically unacceptable container or one which is unstable. The container must be able to withstand such changes in pressure without failure.
Due to the relative high cost of PET material, even slight increases in the weight of the material of the container will result in an excessive increase in its cost, making it less competitive in relation to the glass bottle, thereby resulting in the infeasibility of such a solution to the problem. Additionally, in many instances, container weight is correlated to the amount of the final vacuum present in the container after this fill, cap and cool down procedure. In order to reduce container weight, i.e., “lightweight” the container, thus providing a significant cost savings from a material standpoint, the amount of the final vacuum must be reduced. Typically, the amount of the final vacuum can be reduced through various processing options such as the use of nitrogen dosing technology, minimize head space or reduce fill temperatures. One drawback with the use of nitrogen dosing technology however is that the maximum line speeds achievable with the current technology is limited to roughly 200 containers per minute. Such slower line speeds are seldom acceptable. Additionally, the dosing consistency is not yet at a technological level to achieve efficient operations. Minimizing head space requires more precision during filling, again resulting in slower line speeds. Reducing fill temperatures limits the type of commodity capable of being used and thus is equally disadvantageous.
The above described negative pressure or vacuum within the container has typically been accommodated by the incorporation of structures in the sidewall of the container. These structures are commonly known as vacuum panels. Traditionally, these paneled areas have been semi-rigid by design, unable to accommodate the high levels of negative pressure or vacuum currently generated, particularly in lightweight containers. Currently, hot fill containers typically include substantially rectangular vacuum panels that are designed to collapse inwardly after the container has been filled with hot product. These rectangular vacuum panels are designed so that as product cools, they will deform and move inwardly. While commercially successful, the inward flexing of the rectangular panels caused by the hot fill vacuum creates high stress points at the top and bottom edges of the pressure panels, especially at the upper and lower corners of the panels. These stress points weaken the portions of the sidewall near the edges of the panels, allowing the sidewall to collapse inwardly during handling of the container or when containers are stacked together.
Thus, there is a need for an improved container which is designed to distort inwardly in a controlled manner under the negative pressure or vacuum which results from hot filling so as to accommodate these negative pressures or vacuum and eliminate undesirable deformation in the container yet which allows for lightweighting, accommodates higher fill temperatures and is capable of being easily handled by an end consumer.
With the forgoing in mind, an object of the present invention is to provide novel hot fillable plastic containers which have vacuum absorption panels that flex during hot filling, capping and cooling; which are resistant to unwanted distortion; and which absorb a majority of the negative pressure or vacuum applied to the container.
It is another object of the present invention to provide a hot filled, blow molded, plastic container which provides improved vacuum panels that minimize the stress points on the corners of the vacuum panels, by substantially removing these stress points, and thereby provide lower failure rates.
In function of the above mentioned qualities, associated with its transparency, the proposed container is an extremely inexpensive and efficient means for the container user to promote its product, thus contributing to reinforce the good image of its company in the market. It is therefore an object of this invention to provide such a container.